Inductive effect
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/* Applications */
The '''inductive effect''' in [[chemistry]] is an experimentally observable effect of the transmission of [[charge (physics)|charge]] through a chain of [[atoms]] in a [[molecule]] by [[electrostatic induction]] (IUPAC definition). The net [[polar effect]] exerted by a [[substituent]] is a combination of this inductive effect and the [[mesomeric effect]].
The [[electron cloud]] in a [[Sigma bond|σ-bond]] between two unlike [[atoms]] is not uniform and is slightly displaced towards the more [[Electronegativity|electronegative]] of the two atoms. This causes a permanent state of [[polar bond|bond polarization]], where the more electronegative atom has a slight negative charge(δ-) and the other atom has a slight positive charge(δ+).
If the electronegative atom is then joined to a chain of atoms, usually [[carbon]], the positive charge is relayed to the other atoms in the chain. This is the electron-withdrawing inductive effect, also known as the '''-I effect'''.
Some groups, such as the [[Alkyl group|alkyl]] group are less electron-withdrawing than [[hydrogen]] and are therefore considered as electron-releasing. This is electron releasing character is indicated by the '''+I effect'''.
As the induced change in polarity is less than the original polarity, the inductive effect rapidly dies out, and is significant only over a short distance. The inductive effect is permanent but feeble, as it involves the shift of strongly held σ-bond electrons, and other stronger factors may overshadow this effect.
The inductive effect may be caused by some [[molecules]] also. Relative inductive effects have been experimentally measured with reference to hydrogen.
[[Image:Inductive_effect.PNG|Relative strengths of the inductive effect of various molecules]]
Inductive effects can be measured through the [[Hammett equation]].
== Applications ==
* [[Aliphatic]] carboxylic acids. The [[acidity|strength]] of a [[carboxylic acid]] depends on the extent of its [[ionization]]-the more the ionization, the stronger is the acid. The strength of an acid is denoted by the numerical value of [[Acid dissociation constant|pK<sub>a</sub>]]. In aliphatic acids, the electron releasing inductive effect of the methyl group, increases the electron density on [[oxygen]] and thus hinders the breaking of the O-H bond, which consequently reduces the ionization. Greater ionization in [[formic acid]] when compared to [[acetic acid]] makes formic acid(pK<sub>a</sub>=3.75) stronger than acetic acid(pK<sub>a</sub>=4.76). Monochloroacetic acid(pK<sub>a</sub>=2.82) is stronger than formic acid since the electron-withdrawing effect of chlorine promotes ionization.
* Aromatic carboxylic acids. In [[benzoic acid]], the carbon atoms which are present in the ring are [[Orbital hybridisation|sp<sub>2</sub> hybridised]].As a result, benzoic acid(pK<sub>a</sub>=4.20) is a stronger acid than [[cyclohexane]] [[carboxylic acid]](pK<sub>a</sub>=4.87). Also, electron-withdrawing groups substituted at the [[aromatic ortho substituent|ortho]] and [[Aromatic para substituent|para]] positions, enhance the acid strength.
* Dioic acids. Since the [[carboxyl]] group is itself an electron-withdrawing group, the dioic acids are, in general, stronger than their monocarboxyl analogues.
* In the so-called [[Baker-Nathan effect]] the observed order in electron-releasing alkyl substituents is apparently reversed.
== External links ==
* IUPAC [[Gold Book]] [http://www.iupac.org/goldbook/I03021.pdf definition]
== See also ==
* [[List of publications in chemistry#Organic chemistry|Important publications in organic chemistry]]
[[Category:Physical organic chemistry]]
[[Category:Chemical bonding]]
[[cs:Indukční efekt]]
[[de:Induktiver Effekt]]
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[[it:Effetto induttivo]]
[[sr:Индуктивни ефекат]]